As described in patent document 1, for example, there is conventionally available a vehicle navigation system that displays traffic information about a road along a vehicle's traveling direction without using a route guidance function. This navigation system assumes that a road along the vehicle's traveling direction is a target road of which traffic information should be displayed. Accordingly, the navigation system cannot display traffic information about a road to a destination that does not belong to the road along the vehicle's traveling direction but is expected to be traveled by the vehicle.
By contrast, for example, a vehicle navigation system presented in patent document 2 sets an optimal route to a destination. When traffic congestion occurs on the optimal route, the vehicle navigation system displays traffic congestion information together with the optimal route. This makes it possible to display the traffic information about not only the road along the vehicle's traveling direction, but also the route that differs from this direction but is expected to be traveled by the vehicle up to the destination.                Patent document 1: JP2000-346664 A2        Patent document 2: JP-2785528 B2        
The above-mentioned traffic information such as the traffic congestion information is so important for an occupant to influence the selection of roads to be traveled and needs to be definitely notified to the occupant. Accordingly, it is desirable to provide visually and audibly (i.e., using display guidance and audio guidance) the traffic information such as the traffic congestion information.
When the optimal route is targeted to a destination unfamiliar to the occupant, the occupant needs information such as intersections, junctions, and the like on the route to the destination. It is also desirable to visually and audibly provide the optimal route similarly to the traffic information.
In contrast, when the route is targeted to a destination familiar to the occupant, the occupant does not always need to be visually and audibly guided on the optimal route. In many cases, only a visual indication may be used to sufficiently confirm vehicle's traveling situations on the optimal route. When the optimal route is targeted to the destination familiar to the occupant, visually and audibly providing guidance on the optimal route may cause annoyance or uncomfortable feeling to the occupant.